/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.commons.udf.service;

import org.apache.iotdb.commons.exception.StartupException;
import org.apache.iotdb.commons.file.SystemFileFactory;
import org.apache.iotdb.commons.service.IService;
import org.apache.iotdb.commons.service.ServiceType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class UDFClassLoaderManager implements IService {

    private static final Logger LOGGER = LoggerFactory.getLogger(UDFClassLoaderManager.class);

    private final String libRoot;

    /**
     * The keys in the map are the query IDs of the UDF queries being executed.
     */
    private final Map<Long, UDFClassLoader> queryIdToUDFClassLoaderMap;

    /**
     * activeClassLoader is used to load all classes under libRoot. libRoot may be updated before the
     * user executes CREATE FUNCTION or after the user executes DROP FUNCTION. Therefore, we need to
     * continuously maintain the activeClassLoader so that the classes it loads are always up-to-date.
     */
    private volatile UDFClassLoader activeClassLoader;

    private UDFClassLoaderManager(String libRoot) {
        this.libRoot = libRoot;
        LOGGER.info("UDF lib root: {}", libRoot);
        queryIdToUDFClassLoaderMap = new ConcurrentHashMap<>();
        activeClassLoader = null;
    }

    public void initializeUDFQuery(long queryId) {
        activeClassLoader.acquire();
        queryIdToUDFClassLoaderMap.put(queryId, activeClassLoader);
    }

    public void finalizeUDFQuery(long queryId) {
        UDFClassLoader classLoader = queryIdToUDFClassLoaderMap.remove(queryId);
        try {
            if (classLoader != null) {
                classLoader.release();
            }
        } catch (IOException e) {
            LOGGER.warn(
                    "Failed to close UDFClassLoader (queryId: {}), because {}", queryId, e.toString());
        }
    }

    public UDFClassLoader updateAndGetActiveClassLoader() throws IOException {
        UDFClassLoader deprecatedClassLoader = activeClassLoader;
        activeClassLoader = new UDFClassLoader(libRoot);
        if (deprecatedClassLoader != null) {
            deprecatedClassLoader.markAsDeprecated();
        }
        return activeClassLoader;
    }

    public UDFClassLoader getActiveClassLoader() {
        return activeClassLoader;
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////
    // IService
    /////////////////////////////////////////////////////////////////////////////////////////////////

    @Override
    public void start() throws StartupException {
        try {
            SystemFileFactory.INSTANCE.makeDirIfNecessary(libRoot);
            activeClassLoader = new UDFClassLoader(libRoot);
        } catch (IOException e) {
            throw new StartupException(this.getID().getName(), e.getMessage());
        }
    }

    @Override
    public void stop() {
        // nothing to do
    }

    @Override
    public ServiceType getID() {
        return ServiceType.UDF_CLASSLOADER_MANAGER_SERVICE;
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////
    // singleton instance holder
    /////////////////////////////////////////////////////////////////////////////////////////////////

    private static UDFClassLoaderManager INSTANCE = null;

    public static synchronized UDFClassLoaderManager setupAndGetInstance(String libRoot) {

        if (INSTANCE == null) {
            INSTANCE = new UDFClassLoaderManager(libRoot);
        }
        return INSTANCE;
    }

    public static UDFClassLoaderManager getInstance() {
        return INSTANCE;
    }
}
